1. Field of the Invention
The present invention relates to a technique of fine coal briquetting and, specifically, relates to a pressure briquetting of coal at a normal temperature, and the production thereof.
2. Description of Related Art
A great amount of fine coal are disadvantageously formed in the production process of coal in coal mines and subsequent transportation steps. Particularly, coal of low degree of coalification (brown coal and sub-bituminous coal), which is reserved and mined in great amount in Indonesia or other districts, yield 30 mass % or more of fine coal with a grain size of 2.35 mm or less in the production process and transportation step, to bring about a significant problem. Such fine coal is difficult to be handled with if used as it is and besides it causes fine dusts. This prevents the fine coal from being used in a generating power plant, so that the fine coal is discarded as wastes along with the production of coals. Accordingly, when such fine coal can be agglomerated into briquette products (coal briquette) having both the strength durable to handling during storage and transportation and waterproof against rainfall in the outdoor at a reduced cost, the coal productivity is improved. This leads to an effective use of natural resources and also to a great advantage in various points.
While various reports for the technique of briquetting coal have been presented but they concern coal briquette used in coke material, and have not yet applied to inexpensive common coal or coal of low degree of coalification from an economical view point.
For example, JP-A No.259382/1998 discloses a briquetting method of classifying coal arranged to comprise 85% or more of grains of less than 3 mm size, removing coal with a grain size of 6 mm over, heating the residues at a heating rate of 103xc2x0 C./min or more for 300 to 420xc2x0 C. and then briquetting the same. JP-A No. 3458/1997 discloses a briquetting method of drying coal to a water content of 0 to 2.7%, adding 3 to 5 mass % of tar and/or tar slag to classified and recovered fine coal of 0.3 mm or less, and then briquetting the same by way of a roll briquetting machine. However, both techniques require coal to be heated, suffering from high energy cost. Particularly, in case of processing coal of low degree of coalification having high water content, they also require dewatering and heating. This prevents those techniques from being practically used.
Under the foregoing situations, the present invention aims at providing a method of producing coal briquette free from the drawbacks of the prior art, specifically, a method of producing coal briquette at a reduced energy cost by saving heating step or drying step of coal which was necessary so far for fine coal briquetting, and provide coal briquette which is inexpensive, and has high strength and high waterproof.
In first aspect, the invention provides a coal briquette in which a heavy oil component is coated on the surface of a briquette product obtained by adding and mixing starch to fine coal and pressure briquetting them.
In second aspect, the fine coal contains 15 mass % or more of water content and comprising 50 mass % or more of grains of 5 mm or less.
In third aspect, the addition amount of the starch is from 1 to 10 mass % based on the mass of the briquette product.
In fourth aspect, starch is formed by dissolving starch with hot water into gel and then drying the same into a powdery form.
In fifth aspect, the coating amount of the heavy oil component is from 0.1 to 5 mass % based on the mass of the briquette product.
In sixth aspect, a method of producing coal briquette of the invention has the steps of: adding from 1 to 10 mass parts of powdery starch, to a coal having 15 mass % or more of water content and having 50 mass % or more of grains, with a grain size of 5 mm or less before followed by mixing them, so as to form 100 mass parts of a mixture; and coating the surface of the briquette product with 0.1 to 5 mass parts of a heavy oil component simultaneously with or after pressure briquetting the mixture.
In seventh aspect, the pressure briquetting is conducted by using a double roll briquetting machine in which concave portions are formed on the roll surface.
In the present specification, xe2x80x9cbriquette productxe2x80x9d is defined as a product only as pressure briquetting but not yet applied with coating treatment, and also xe2x80x9ccoal briquettexe2x80x9d is defined as xe2x80x9cbriquette productxe2x80x9d further applied with coating treatment.
When starch is added and mixed to the fine coal, starch is uniformly dispersed into gaps between the coal particles. Then, the mixture is briquetted by pressure, and thereby a portion of the water content of the coal is leached to the surface of the coal particles. These water content and the starch are heated to a temperature of about 60xc2x0 C. by the heat of friction upon pressure briquetting, converting into starch. Thereafter, they, through being gelled after cooling, firmly adhere the coal particles to each other. That is, the starch functions as a binder. In addition, the heavy oil component is coated on the surface of the briquette product as a coating agent to thereby form a coated coal briquette. This allows the heavy oil component, which is a hydrophobic material solid or liquid at normal temperature, to clog pores on the surface of the briquette product to inhibit water from intruding into the inside of the coal briquette, e.g. when the coal briquette is exposed to water of rainfall at the outdoor. This prevents gelled starch from being softened with an excess water content. And this also maintains adherence between coal particles to each other, keeping the strength of the coal briquette for a long period of time, even in the storage or transportation of the coal briquette in an external environment. That is, an obtained briquette product is excellent in waterproof.
The use of the fine coal with a water content of 15 mass % or more and, more preferably, 25 mass % or more allows a sufficient amount of water content to be leached out to the surface of coal particles upon pressure briquetting. This allows starch to be gelled sufficiently to thereby further increase the strength of adherance between coal particles to each other. Further, arranging the grain distribution such that 50% or more, more preferably, 60 mass % or more and, further preferably, 70 mass % or more, and the most preferably, 80 mass % or more of the fine coal a grain size of which is 5 mm or less, permits of the increase of the number of contacts between the particles to each other and relative to the starch as the binder, as well as of the increase of the strength of the coal briquette.
When the addition amount of starch is less than 1 mass %, the amount of the gelled starch is insufficient, causing to lower the strength of the coal briquette. On the other hand, considering that the effect of improving the strength of the coal briquette is small by addition in excess of 10 mass % and it is wasteful, addition amount is, preferably, 1 to 10 mass % and, more preferably, 3 to 5 mass %.
For the starch added to the fine coal, similar effect can also be obtained by using starch which was previously dissolved by hot water and formed into gel and then dried to a powdery state.
When the coating amount of the heavy oil component to the surface of the briquette product is less than 0.1 mass % based on the mass of the briquette product, the coating is not complete and water is liable to intrude from the outside to the inside of the briquette product to possibly lower the strength of the briquette product. On the other hand, considering that coating in excess of 5 mass % has no more effect and is wasteful, it is preferably from 0.1 to 5 mass % and, more preferably, from 0.5 to 3 mass %.
For conducting the pressure briquetting, for example, by a double roll briquetting machine having concaves at the roll surface, since a sufficient pressing force is applied as far as the inside of the briquette product, a sufficient amount of water content is leached out from the fine coal for the entire briquette product and, in addition, temperature elevation due to frictional force is made uniform to promote gelation of starch.
Other and further objects, features and advantages of the invention will appear more fully from the following description.